In spite of the fact that coronary revascularization procedures (Vineberg and vein bypass grafts) are widely used, no definitive hemodynamic proof is presently available to indicate that such surgery indeed increases myocardial blood flow. It is the objective of this study to evaluate regional myocardial blood flow in patients prior to and following myocardial revascularization. A scintillation camera, with computer processing of data, will be installed in the catheterization laboratory and used in conjunction with coronary arteriography. This will make it possible to obtain quantitative data on regional myocardial blood flow, following the intracoronary administration of Xenon-133 dissolved in saline. Data will be collected on magnetic tape, which will be processed by a Control Data 3300 computer. Programs will be written to analyze the washout curves over numerous areas of the myocardium, thus allowing the computation of regional myocardial blood flow. With this method, it should be possible to obtain objective data about the redistribution of regional myocardial blood flow following myocardial revascularization. Without this information, the efficacy of modern coronary surgery remains in doubt.